Evaluation of an Aerosol Activation Parameterization Christos Fountoukis
- Slides: 12
Evaluation of an Aerosol Activation Parameterization Christos Fountoukis April 19, 2004 EAS: Atmospheric Chemistry Term Paper
Summary • The new aerosol activation parameterization • The adiabatic cloud parcel model • Evaluation of the parameterization for a wide range of: – Chemical variability – CCN (cloud condensation nuclei) concentrations – Updraft velocities, temperatures, pressures • Conclusions
Aerosol activation parameterization • Developed in two steps: – Representation of the aerosol number and the chemical composition distribution with respect to size and calculation of the CCN spectrum – Determination of the maximum supersaturation by a numerical solution of an algebraic equation and calculation of droplet number concentration from the supersaturation spectrum
Sectional representation of size distribution
CCN spectrum
Droplet number concentration estimation Once the maximum parcel supersaturation, smax, is known, the number of CCN that will activate into drops, Nd, is given by
Adiabatic cloud parcel model • Based upon the parcel model described by Seinfeld and Pandis, (1998). • Resolves numerically a set of differential equations that describe the rate of growth of a drop of diameter Dp • Determines the droplet diameter at the time of maximum supersaturation
Simulations for different conditions • • • Ntotal (cm-3) σ Dp, g (μm) W (m/s) Cloud height (m) Chemical composition 100, 500, 1000, 5000, 10000 1. 1, 1. 2, 1. 5, 2. 0, 2. 5 0. 025, 0. 05, 0. 75, 0. 25 0. 1, 0. 3, 1. 0, 3. 0 500 (NH 4)2 SO 4: 100%, (NH 4)2 SO 4: 50%-insoluble: 50%, Na. Cl: 100%, Na. Cl: 25% - insoluble: 75 • • Accommodation coefficient Pressure (mbar) Relative humidity Temperature (K) 0. 005, 0. 01, 0. 1, 1 800, 1000 90%, 98% 273, 303
Results
Results (2)
Results (3)
Conclusions • For the wide variety of aerosol characteristics, very good agreement between the two models • Systematic biases for: – Insoluble species – Species with low accommodation coefficient • The open structure of the parameterization allows for further extension (include condensable gases, organics, etc. )